(1) Field of the Invention
The present invention relates to a connection for a fiber-reinforced spoke. The present invention is particularly related to the spoke of a vehicle wheel, where the bracing element comprises the rim or hub of the vehicle wheel.
(2) Description of the Related Art
Heretofore, the vast majority of bicycle wheels have been constructed using steel wire spokes with one headed end for connection with the bicycle hub and an opposing end that is directly threaded to accept a spoke nipple that engages the rim. By adjusting the threaded connection between the spoke and the nipple, the overall length of the spoke may be shortened or lengthened to create a balanced pretension in the spokes of the wheel.
Bicycle spokes serve as structural tensile elements where the tension of the spoke is resisted by the hoop compression of the outer rim hoop to create a remarkably efficient wheel structure for handling the loads associated with the operation of the bicycle. The technology of conventional bicycle spokes has remained unchanged for the better part of a century.
Cyclists are continually striving to reduce the weight and increase the efficiency of their bicycle, especially rotating components such as the bicycle wheel. However, the steel spokes of conventional bicycle wheels are quite heavy and add significant weight to the wheel assembly.
In addition to their excessive weight, steel bicycle spokes have poor vibration-damping characteristics and tend to be very efficient at transmitting road vibration to the rider. By transmitting vibration, rather than absorbing it, the conventional steel-spoke bicycle wheel lacks in rider comfort and control.
In attempt to reduce weight, many makers of high-end wheels have resorted to forming their spokes from thinner gage steel wire. This causes the stress in the spoke to increase and makes the wheel more prone to spoke failure due to fatigue. The thinner steel wire has lower tensile stiffness, which can contribute to a reduced side-to-side stiffness of the wheel.
In the last 30 years, great strides have been made in the development of very lightweight materials that also have excellent tensile characteristics. Some of the most attractive of these materials include high-strength fibers, such as carbon fiber, aramid fiber, liquid crystal fiber, PBO® fiber and the like. However, when attempting to utilize them as spokes in bicycle wheel construction, these fibrous materials are far more difficult to efficiently couple or terminate than their conventional steel-wire counterparts. In the few cases where these high strength spokes have successfully been utilized in bicycle wheels, their cost and complexity has been very great. This is the primary reason that the vast majority of bicycle wheels are still constructed using steel spokes.
While there have been some attempts to produce fiber reinforced spokes for bicycles, these spokes have been molded as a complete unit. In the case where thermoset matrix resins are utilized, this results in very long molding cycles because the fiber must be carefully layed up and the resin needs long residence time in the mold in order to catalyze and harden. Also, since the entire spoke is molded, the corresponding mold tool is very large and expensive. Further, since the cycle times are slow, a large number of these tools are required in order to achieve sufficient production throughput. Alternatively, in the case of molding a single thermoplastic spoke (such as U.S. Pat. No. 5,779,323), this is commonly achieved through injection molding, a fluid flow process that only accommodates short reinforcement fibers and not the continuous fibers as defined herein. These short fibers have far inferior tensile properties in comparison with continuous fibers.
Accordingly, it is an objective of the present invention to overcome the forgoing disadvantages and to provide a spoke and a connection system for such a spoke that is strong, lightweight and inexpensive to produce.
It is a further object of the present invention to facilitate the utilization of high strength fiber-reinforced materials in spoke and/or tensile element construction and to create a high strength connecting system for such spokes.
It is a still further objective of the present invention to provide a connection system for spokes and/or tensile elements that has minimal mechanical complexity and is easily serviceable, and permits easy installation and removal of such spokes and/or tensile elements.
Further objects and advantages of the present invention will appear hereinbelow.